Reduction of sampling rates in lidar systems

ABSTRACT

A LIDAR system has a transmitter that outputs a system output signal from the LIDAR system. The LIDAR system also includes electronics that control a frequency of the system output signal over a series of cycles. The cycles include multiple data periods. The electronics change the frequency of the system output signal at a first rate during a first one of the data periods. The electronics change the frequency of the system output signal at a second rate during a second one of the data periods. The second rate is different from the first rate.

FIELD

The invention relates to optical devices. In particular, the invention relates to LIDAR systems.

BACKGROUND

Many LIDAR systems include one or more Analog-to-Digital Converters (ADC) that each receives a beating signal. The high frequencies of these beating signals requires that the Analog-to-Digital Converters (ADC) be sampled at high rates. However, the price and power consumption of the commercially available Analog-to-Digital Converters (ADC) are directly related to this sampling rate. As a result, the high sampling rates associated with the one or more Analog-to-Digital Converters (ADC) in LIDAR systems can make these systems impractical for commercial production. As a result, there is a need for practical LIDAR systems.

SUMMARY

A LIDAR system has a transmitter that outputs a system output signal from the LIDAR system. The LIDAR system also includes electronics that control a frequency of the system output signal over a series of cycles. The cycles include multiple data periods. The electronics change the frequency of the system output signal at a first rate during a first one of the data periods. The electronics change the frequency of the system output signal at a second rate during a second one of the data periods. The second rate is different from the first rate.

A LIDAR system includes an Analog-to-Digital Converter (ADC) that receives a beating signal that beats a first signal against a second signal. The first signal is generated from light that has exited from the LIDAR system and returned to the LIDAR system after being reflected by an object located outside of the LIDAR system. The second signal is generated from light that has not exited from the LIDAR system. A frequency of the beating signal has a frequency contribution from a separation between the LIDAR system and the object. Electronics generate multiple first possible frequency values that are each a candidate for a value of the frequency contribution.

Operating a LIDAR system can include receiving a beating signal at an Analog-to-Digital Converter (ADC). The beating signal beats a first signal against a second signal. The first signal is generated from light that has exited from the LIDAR system and returned to the LIDAR system after being reflected by an object located outside of the LIDAR system. The second signal is generated from light that has not exited from the LIDAR system. A frequency of the beating signal has a frequency contribution from a separation between the LIDAR system and the object. Operating the LIDAR system can also include generating multiple first possible frequency values that are each a candidate for the value of the frequency contribution.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a topview of a schematic of a LIDAR system that includes or consists of a LIDAR chip that outputs a LIDAR output signal and receives a LIDAR input signal on a common waveguide.

FIG. 1B is a topview of a schematic of a LIDAR system that includes or consists of a LIDAR chip that outputs a LIDAR output signal and receives a LIDAR input signal on different waveguides.

FIG. 1C is a topview of a schematic of another embodiment of a LIDAR system that that includes or consists of a LIDAR chip that outputs a LIDAR output signal and receives multiple LIDAR input signals on different waveguides.

FIG. 1D is a topview of a schematic of a LIDAR system that includes a LIDAR chip that receives an outgoing LIDAR signal from a light source located off the LIDAR chip.

FIG. 2 is a topview of an example of a LIDAR adapter that is suitable for use with the LIDAR chip of FIG. 1B.

FIG. 3 is a topview of an example of a LIDAR adapter that is suitable for use with the LIDAR chip of FIG. 1C.

FIG. 4 is a topview of an example of a LIDAR system that includes the LIDAR chip of FIG. 1A and the LIDAR adapter of FIG. 2 on a common support.

FIG. 5A illustrates an example of a processing component suitable for use with the LIDAR systems.

FIG. 5B provides a schematic of electronics that are suitable for use with a processing component constructed according to FIG. 5A.

FIG. 5C illustrates another example of a processing component suitable for use with the LIDAR systems.

FIG. 5D provides a schematic of electronics that are suitable for use with a processing component constructed according to FIG. 5C.

FIG. 5E is a graph of frequency versus time for one of the channels included in a LIDAR output signal.

FIG. 5F illustrates a frequency spectrum for use with the LIDAR system.

FIG. 6 is a cross-section of portion of a LIDAR chip that includes a waveguide on a silicon-on-insulator platform.

DESCRIPTION

A LIDAR system transmits a system output signal. Light from the system output signal can be reflected by an object located outside of the LIDAR system. A portion of the reflected light can return to the LIDAR system. The LIDAR system can combine the returned light with another light signal to form a beating signal. The LIDAR system uses the beating signal to generate a data signal that is an electrical signal and is also beating. The data signal can be received by an Analog-to-Digital Converters (ADC) that outputs a digital data signal. The LIDAR system includes electronics that use the digital data signal to generate LIDAR data (radial velocity and/or distance between a LIDAR system and an object external to the LIDAR system).

During operation of the LIDAR system, the LIDAR system proceeds through a series of cycles. During each cycle, the LIDAR system illuminates a sample region. The LIDAR data for objects located in the illuminated sample region can be generated from each cycle. Each cycle includes multiple data periods and the electronics control the frequency of the system output signal during each of the different data periods. For instance, in at least two of the data periods, the electronics can change the frequency of the system output signal for the duration of the data period. The rate of the frequency change during the two data periods can be selected such that the LIDAR data can be successfully quantified even when the Analog-to-Digital Converters (ADC) are undersampled. As a result, the LIDAR system can undersample the one or more Analog-to-Digital Converters (ADC). Since undersampling reduces the ADC sampling rate required by the LIDAR system relative to prior LIDAR systems. The reduced sampling rates reduce the costs and/or power consumption of the LIDAR system.

FIG. 1A is a topview of a schematic of a LIDAR chip that can serve as a LIDAR system or can be included in a LIDAR system that includes components in addition to the LIDAR chip. The LIDAR chip can include a Photonic Integrated Circuit (PIC) and can be a Photonic Integrated Circuit chip. The LIDAR chip includes a light source 10 that outputs an outgoing LIDAR signal. A suitable light source 10 includes, but is not limited to, semiconductor lasers such as External Cavity Lasers (ECLs), Distributed Feedback lasers (DFBs), Discrete Mode (DM) lasers and Distributed Bragg Reflector lasers (DBRs).

The LIDAR chip also includes a utility waveguide 12 that receives the outgoing LIDAR signal from the light source 10. The utility waveguide 12 terminates at a facet 14 and carries the outgoing LIDAR signal to the facet 14. The facet 14 can be positioned such that the outgoing LIDAR signal traveling through the facet 14 exits the LIDAR chip and serves as a LIDAR output signal. For instance, the facet 14 can be positioned at an edge of the chip so the outgoing LIDAR signal traveling through the facet 14 exits the chip and serves as the LIDAR output signal. In some instances, the portion of the LIDAR output signal that has exited from the LIDAR chip can also be considered a system output signal. As an example, when the exit of the LIDAR output signal from the LIDAR chip is also an exit of the LIDAR output signal from the LIDAR system, the LIDAR output signal can also be considered a system output signal. When the portion of the LIDAR output signal serves as a system output signal the facet 14 can serve as the transmitter of the LIDAR system.

The LIDAR output signal travels away from the LIDAR system through free space in the atmosphere in which the LIDAR system is positioned. The LIDAR output signal may be reflected by one or more objects in the path of the LIDAR output signal. When the LIDAR output signal is reflected, at least a portion of the reflected light travels back toward the LIDAR chip as a LIDAR input signal. In some instances, the LIDAR input signal can also be considered a system return signal. As an example, when the exit of the LIDAR output signal from the LIDAR chip is also an exit of the LIDAR output signal from the LIDAR system, the LIDAR input signal can also be considered a system return signal.

The LIDAR input signals can enter the utility waveguide 12 through the facet 14. The portion of the LIDAR input signal that enters the utility waveguide 12 serves as an incoming LIDAR signal. The utility waveguide 12 carries the incoming LIDAR signal to a splitter 16 that moves a portion of the outgoing LIDAR signal from the utility waveguide 12 onto a comparative waveguide 18 as a comparative signal. The comparative waveguide 18 carries the comparative signal to a processing component 22 for further processing. Although FIG. 1A illustrates a directional coupler operating as the splitter 16, other signal tapping components can be used as the splitter 16. Suitable splitters 16 include, but are not limited to, directional couplers, optical couplers, y-junctions, tapered couplers, and Multi-Mode Interference (MIMI) devices.

The utility waveguide 12 also carrier the outgoing LIDAR signal to the splitter 16. The splitter 16 moves a portion of the outgoing LIDAR signal from the utility waveguide 12 onto a reference waveguide 20 as a reference signal. The reference waveguide 20 carries the reference signal to the processing component 22 for further processing.

The percentage of light transferred from the utility waveguide 12 by the splitter 16 can be fixed or substantially fixed. For instance, the splitter 16 can be configured such that the power of the reference signal transferred to the reference waveguide 20 is an outgoing percentage of the power of the outgoing LIDAR signal or such that the power of the comparative signal transferred to the comparative waveguide 18 is an incoming percentage of the power of the incoming LIDAR signal. In many splitters 16, such as directional couplers and multimode interferometers (MMIs), the outgoing percentage is equal or substantially equal to the incoming percentage. In some instances, the outgoing percentage is greater than 30%, 40%, or 49% and/or less than 51%, 60%, or 70% and/or the incoming percentage is greater than 30%, 40%, or 49% and/or less than 51%, 60%, or 70%. A splitter 16 such as a multimode interferometers (MMIs) generally provides an outgoing percentage and an incoming percentage of 50% or about 50%. However, multimode interferometers (MMIs) can be easier to fabricate in platforms such as silicon-on-insulator platforms than some alternatives. In one example, the splitter 16 is a multimode interferometer (MMI) and the outgoing percentage and the incoming percentage are 50% or substantially 50%. As will be described in more detail below, the processing component 22 combines the comparative signal with the reference signal to form a composite signal that carries LIDAR data for a sample region on the field of view. Accordingly, the composite signal can be processed so as to extract LIDAR data (radial velocity and/or distance between a LIDAR system and an object external to the LIDAR system) for the sample region.

The LIDAR chip can include a control branch for controlling operation of the light source 10. The control branch includes a splitter 26 that moves a portion of the outgoing LIDAR signal from the utility waveguide 12 onto a control waveguide 28. The coupled portion of the outgoing LIDAR signal serves as a tapped signal. Although FIG. 1A illustrates a directional coupler operating as the splitter 26, other signal tapping components can be used as the splitter 26. Suitable splitters 26 include, but are not limited to, directional couplers, optical couplers, y-junctions, tapered couplers, and Multi-Mode Interference (MIMI) devices.

The control waveguide 28 carries the tapped signal to control components 30. The control components can be in electrical communication with electronics 32. During operation, the electronics 32 can adjust the frequency of the outgoing LIDAR signal in response to output from the control components. An example of a suitable construction of control components is provided in U.S. patent application Ser. No. 15/977,957, filed on 11 May 2018, entitled “Optical Sensor Chip,” and incorporated herein in its entirety.

The LIDAR system can be modified so the incoming LIDAR signal and the outgoing LIDAR signal can be carried on different waveguides. For instance, FIG. 1B is a topview of the LIDAR chip of FIG. 1A modified such that the incoming LIDAR signal and the outgoing LIDAR signal are carried on different waveguides. The outgoing LIDAR signal exits the LIDAR chip through the facet 14 and serves as the LIDAR output signal. When light from the LIDAR output signal is reflected by an object external to the LIDAR system, at least a portion of the reflected light returns to the LIDAR chip as a first LIDAR input signal. The first LIDAR input signals enters the comparative waveguide 18 through a facet 34 and serves as the comparative signal. The comparative waveguide 18 carries the comparative signal to a processing component 22 for further processing. As described in the context of FIG. 1A, the reference waveguide 20 carries the reference signal to the processing component 22 for further processing. As will be described in more detail below, the processing component 22 combines the comparative signal with the reference signal to form a composite signal that carries LIDAR data for a sample region on the field of view.

The LIDAR chips can be modified to receive multiple LIDAR input signals. For instance, FIG. 1C illustrates the LIDAR chip of FIG. 1B modified to receive two LIDAR input signals. A splitter 40 is configured to place a portion of the reference signal carried on the reference waveguide 20 on a first reference waveguide 42 and another portion of the reference signal on a second reference waveguide 44. Accordingly, the first reference waveguide 42 carries a first reference signal and the second reference waveguide 44 carries a second reference signal. The first reference waveguide 42 carries the first reference signal to a first processing component 46 and the second reference waveguide 44 carries the second reference signal to a second processing component 48. Examples of suitable splitters 40 include, but are not limited to, y-junctions, optical couplers, and multi-mode interference couplers (MMIs).

The outgoing LIDAR signal exits the LIDAR chip through the facet 14 and serves as the LIDAR output signal. When light from the LIDAR output signal is reflected by one or more object located external to the LIDAR system, at least a portion of the reflected light returns to the LIDAR chip as a first LIDAR input signal. The first LIDAR input signals enters the comparative waveguide 18 through the facet 34 and serves as a first comparative signal. The comparative waveguide 18 carries the first comparative signal to a first processing component 46 for further processing.

Additionally, when light from the LIDAR output signal is reflected by one or more object located external to the LIDAR system, at least a portion of the reflected signal returns to the LIDAR chip as a second LIDAR input signal. The second LIDAR input signals enters a second comparative waveguide 50 through a facet 52 and serves as a second comparative signal carried by the second comparative waveguide 50. The second comparative waveguide 50 carries the second comparative signal to a second processing component 48 for further processing.

Although the light source 10 is shown as being positioned on the LIDAR chip, all or a portion of the light source 10 can be located off the LIDAR chip. For instance, the utility waveguide 12 can terminate at a second facet through which the outgoing LIDAR signal can enter the utility waveguide 12 from a light source located off the LIDAR chip. As an example, FIG. 1D illustrates the LIDAR system of FIG. 1A modified to include a light source 10 located off of the LIDAR chip. The utility waveguide 12 includes a second facet 53. An optical link 54, such as one or more optical fibers, carries the outgoing LIDAR signal to the second facet 53 of the utility waveguide 12. The optical link 54 is aligned with the utility waveguide 12 such that an outgoing LIDAR signal generated by the light source 10 can enter the utility waveguide 12 through the second facet 53. An alignment mechanism 55 such as a fiber block can provide alignment between the optical link 54 and the utility waveguide 12. An optical amplifier 57 can optionally be positioned along the optical link so as to amplify the outgoing LIDAR signal. When the light source is external to the LIDAR chip, suitable light sources include, but are not limited to, semiconductor lasers such as External Cavity Lasers (ECLs), Distributed Feedback lasers (DFBs), Discrete Mode (DM) lasers and Distributed Bragg Reflector lasers (DBRs). In some instances, the LIDAR system includes one or more lenses (not shown) that couple the outgoing LIDAR source into the amplifier 57 or into the utility waveguide 12.

In some instances, a LIDAR chip constructed according to FIG. 1B or FIG. 1C is used in conjunction with a LIDAR adapter. In some instances, the LIDAR adapter can be physically optically positioned between the LIDAR chip and the one or more reflecting objects and/or the field of view in that an optical path that the first LIDAR input signal(s) and/or the LIDAR output signal travels from the LIDAR chip to the field of view passes through the LIDAR adapter. Additionally, the LIDAR adapter can be configured to operate on the first LIDAR input signal and the LIDAR output signal such that the first LIDAR input signal and the LIDAR output signal travel on different optical pathways between the LIDAR adapter and the LIDAR chip but on the same optical pathway between the LIDAR adapter and a reflecting object in the field of view.

An example of a LIDAR adapter that is suitable for use with the LIDAR chip of FIG. 1B is illustrated in FIG. 2 . The LIDAR adapter includes multiple components positioned on a base. For instance, the LIDAR adapter includes a circulator 100 positioned on a base 102. The illustrated optical circulator 100 includes three ports and is configured such that light entering one port exits from the next port. For instance, the illustrated optical circulator includes a first port 104, a second port 106, and a third port 108. The LIDAR output signal enters the first port 104 from the utility waveguide 12 of the LIDAR chip and exits from the second port 106.

The LIDAR adapter can be configured such that the output of the LIDAR output signal from the second port 106 can also serve as the output of the LIDAR output signal from the LIDAR adapter and accordingly from the LIDAR system. As a result, the LIDAR output signal can be output from the LIDAR adapter such that the LIDAR output signal is traveling toward a sample region in the field of view. Accordingly, in some instances, the portion of the LIDAR output signal that has exited from the LIDAR adapter can also be considered the system output signal. As an example, when the exit of the LIDAR output signal from the LIDAR adapter is also an exit of the LIDAR output signal from the LIDAR system, the LIDAR output signal can also be considered a system output signal. When the LIDAR output signal serves as a system output signal, the second port 106 can serve as a transmitter for the LIDAR system.

The LIDAR output signal output from the LIDAR adapter includes, consists of, or consists essentially of light from the LIDAR output signal received from the LIDAR chip. Accordingly, the LIDAR output signal output from the LIDAR adapter may be the same or substantially the same as the LIDAR output signal received from the LIDAR chip. However, there may be differences between the LIDAR output signal output from the LIDAR adapter and the LIDAR output signal received from the LIDAR chip. For instance, the LIDAR output signal can experience optical loss as it travels through the LIDAR adapter and/or the LIDAR adapter can optionally include an amplifier configured to amplify the LIDAR output signal as it travels through the LIDAR adapter.

When one or more objects in the sample region reflect the LIDAR output signal, at least a portion of the reflected light travels back to the circulator 100 as a system return signal. The system return signal enters the circulator 100 through the second port 106. FIG. 2 illustrates the LIDAR output signal and the system return signal traveling between the LIDAR adapter and the sample region along the same optical path.

The system return signal exits the circulator 100 through the third port 108 and is directed to the comparative waveguide 18 on the LIDAR chip. Accordingly, all or a portion of the system return signal can serve as the first LIDAR input signal and the first LIDAR input signal includes or consists of light from the system return signal. Accordingly, the LIDAR output signal and the first LIDAR input signal travel between the LIDAR adapter and the LIDAR chip along different optical paths.

As is evident from FIG. 2 , the LIDAR adapter can include optical components in addition to the circulator 100. For instance, the LIDAR adapter can include components for directing and controlling the optical path of the LIDAR output signal and the system return signal. As an example, the adapter of FIG. 2 includes an optional amplifier 110 positioned so as to receive and amplify the LIDAR output signal before the LIDAR output signal enters the circulator 100. The amplifier 110 can be operated by the electronics 32 allowing the electronics 32 to control the power of the LIDAR output signal.

FIG. 2 also illustrates the LIDAR adapter including an optional first lens 112 and an optional second lens 114. The first lens 112 can be configured to couple the LIDAR output signal to a desired location. In some instances, the first lens 112 is configured to focus or collimate the LIDAR output signal at a desired location. In one example, the first lens 112 is configured to couple the LIDAR output signal on the first port 104 when the LIDAR adapter does not include an amplifier 110. As another example, when the LIDAR adapter includes an amplifier 110, the first lens 112 can be configured to couple the LIDAR output signal on the entry port to the amplifier 110. The second lens 114 can be configured to couple the LIDAR output signal at a desired location. In some instances, the second lens 114 is configured to focus or collimate the LIDAR output signal at a desired location. For instance, the second lens 114 can be configured to couple the LIDAR output signal the on the facet 34 of the comparative waveguide 18.

The LIDAR adapter can also include one or more direction changing components such as mirrors. FIG. 2 illustrates the LIDAR adapter including a mirror as a direction-changing component 116 that redirects the system return signal from the circulator 100 to the facet 20 of the comparative waveguide 18.

The LIDAR chips include one or more waveguides that constrains the optical path of one or more light signals. While the LIDAR adapter can include waveguides, the optical path that the system return signal and the LIDAR output signal travel between components on the LIDAR adapter and/or between the LIDAR chip and a component on the LIDAR adapter can be free space. For instance, the system return signal and/or the LIDAR output signal can travel through the atmosphere in which the LIDAR chip, the LIDAR adapter, and/or the base 102 is positioned when traveling between the different components on the LIDAR adapter and/or between a component on the LIDAR adapter and the LIDAR chip. As a result, optical components such as lenses and direction changing components can be employed to control the characteristics of the optical path traveled by the system return signal and the LIDAR output signal on, to, and from the LIDAR adapter.

Suitable bases 102 for the LIDAR adapter include, but are not limited to, substrates, platforms, and plates. Suitable substrates include, but are not limited to, glass, silicon, and ceramics. The components can be discrete components that are attached to the substrate. Suitable techniques for attaching discrete components to the base 102 include, but are not limited to, epoxy, solder, and mechanical clamping. In one example, one or more of the components are integrated components and the remaining components are discrete components. In another example, the LIDAR adapter includes one or more integrated amplifiers and the remaining components are discrete components.

The LIDAR system can be configured to compensate for polarization. Light from a laser source is typically linearly polarized and hence the LIDAR output signal is also typically linearly polarized. Reflection from an object may change the angle of polarization of the returned light. Accordingly, the system return signal can include light of different linear polarization states. For instance, a first portion of a system return signal can include light of a first linear polarization state and a second portion of a system return signal can include light of a second linear polarization state. The intensity of the resulting composite signals is proportional to the square of the cosine of the angle between the comparative and reference signal polarization fields. If the angle is 90 degrees, the LIDAR data can be lost in the resulting composite signal. However, the LIDAR system can be modified to compensate for changes in polarization state of the LIDAR output signal.

FIG. 3 illustrates the LIDAR system of FIG. 3 modified such that the LIDAR adapter is suitable for use with the LIDAR chip of FIG. 1C. The LIDAR adapter includes a beamsplitter 120 that receives the system return signal from the circulator 100. The beamsplitter 120 splits the system return signal into a first portion of the system return signal and a second portion of the system return signal. Suitable beamsplitters include, but are not limited to, Wollaston prisms, and MEMS-based beamsplitters.

The first portion of the system return signal is directed to the comparative waveguide 18 on the LIDAR chip and serves as the first LIDAR input signal described in the context of FIG. 1C. The second portion of the system return signal is directed a polarization rotator 122. The polarization rotator 122 outputs a second LIDAR input signal that is directed to the second input waveguide 76 on the LIDAR chip and serves as the second LIDAR input signal.

The beamsplitter 120 can be a polarizing beam splitter. One example of a polarizing beamsplitter is constructed such that the first portion of the system return signal has a first polarization state but does not have or does not substantially have a second polarization state and the second portion of the system return signal has a second polarization state but does not have or does not substantially have the first polarization state. The first polarization state and the second polarization state can be linear polarization states and the second polarization state is different from the first polarization state. For instance, the first polarization state can be TE and the second polarization state can be TM or the first polarization state can be TM and the second polarization state can be TE. In some instances, the laser source can linearly polarized such that the LIDAR output signal has the first polarization state. Suitable beamsplitters include, but are not limited to, Wollaston prisms, and MEMs-based polarizing beamsplitters.

A polarization rotator can be configured to change the polarization state of the first portion of the system return signal and/or the second portion of the system return signal. For instance, the polarization rotator 122 shown in FIG. 3 can be configured to change the polarization state of the second portion of the system return signal from the second polarization state to the first polarization state. As a result, the second LIDAR input signal has the first polarization state but does not have or does not substantially have the second polarization state. Accordingly, the first LIDAR input signal and the second LIDAR input signal each have the same polarization state (the first polarization state in this example). Despite carrying light of the same polarization state, the first LIDAR input signal and the second LIDAR input signal are associated with different polarization states as a result of the use of the polarizing beamsplitter. For instance, the first LIDAR input signal carries the light reflected with the first polarization state and the second LIDAR input signal carries the light reflected with the second polarization state. As a result, the first LIDAR input signal is associated with the first polarization state and the second LIDAR input signal is associated with the second polarization state.

Since the first LIDAR input signal and the second LIDAR carry light of the same polarization state, the comparative signals that result from the first LIDAR input signal have the same polarization angle as the comparative signals that result from the second LIDAR input signal.

Suitable polarization rotators include, but are not limited to, rotation of polarization-maintaining fibers, Faraday rotators, half-wave plates, MEMs-based polarization rotators and integrated optical polarization rotators using asymmetric y-branches, Mach-Zehnder interferometers and multi-mode interference couplers.

Since the outgoing LIDAR signal is linearly polarized, the first reference signals can have the same linear polarization state as the second reference signals. Additionally, the components on the LIDAR adapter can be selected such that the first reference signals, the second reference signals, the comparative signals and the second comparative signals each have the same polarization state. In the example disclosed in the context of FIG. 3 , the first comparative signals, the second comparative signals, the first reference signals, and the second reference signals can each have light of the first polarization state.

As a result of the above configuration, first composite signals generated by the first processing component 46 and second composite signals generated by the second processing component 48 each results from combining a reference signal and a comparative signal of the same polarization state and will accordingly provide the desired beating between the reference signal and the comparative signal. For instance, the composite signal results from combining a first reference signal and a first comparative signal of the first polarization state and excludes or substantially excludes light of the second polarization state or the composite signal results from combining a first reference signal and a first comparative signal of the second polarization state and excludes or substantially excludes light of the first polarization state. Similarly, the second composite signal includes a second reference signal and a second comparative signal of the same polarization state will accordingly provide the desired beating between the reference signal and the comparative signal. For instance, the second composite signal results from combining a second reference signal and a second comparative signal of the first polarization state and excludes or substantially excludes light of the second polarization state or the second composite signal results from combining a second reference signal and a second comparative signal of the second polarization state and excludes or substantially excludes light of the first polarization state.

The above configuration results in the LIDAR data for a single sample region in the field of view being generated from multiple different composite signals (i.e. first composite signals and the second composite signal) from the sample region. In some instances, determining the LIDAR data for the sample region includes the electronics combining the LIDAR data from different composite signals (i.e. the composite signals and the second composite signal). Combining the LIDAR data can include taking an average, median, or mode of the LIDAR data generated from the different composite signals. For instance, the electronics can average the distance between the LIDAR system and the reflecting object determined from the composite signal with the distance determined from the second composite signal and/or the electronics can average the radial velocity between the LIDAR system and the reflecting object determined from the composite signal with the radial velocity determined from the second composite signal.

In some instances, determining the LIDAR data for a sample region includes the electronics identifying one or more composite signals (i.e. the composite signal and/or the second composite signal) as the source of the LIDAR data that is most represents reality (the representative LIDAR data). The electronics can then use the LIDAR data from the identified composite signal as the representative LIDAR data to be used for additional processing. For instance, the electronics can identify the signal (composite signal or the second composite signal) with the larger amplitude as having the representative LIDAR data and can use the LIDAR data from the identified signal for further processing by the LIDAR system. In some instances, the electronics combine identifying the composite signal with the representative LIDAR data with combining LIDAR data from different LIDAR signals. For instance, the electronics can identify each of the composite signals with an amplitude above an amplitude threshold as having representative LIDAR data and when more than two composite signals are identified as having representative LIDAR data, the electronics can combine the LIDAR data from each of identified composite signals. When one composite signal is identified as having representative LIDAR data, the electronics can use the LIDAR data from that composite signal as the representative LIDAR data. When none of the composite signals is identified as having representative LIDAR data, the electronics can discard the LIDAR data for the sample region associated with those composite signals.

Although FIG. 3 is described in the context of components being arranged such that the first comparative signals, the second comparative signals, the first reference signals, and the second reference signals each have the first polarization state, other configurations of the components in FIG. 3 can arranged such that the composite signals result from combining a reference signal and a comparative signal of the same linear polarization state and the second composite signal results from combining a reference signal and a comparative signal of the same linear polarization state. For instance, the beamsplitter 120 can be constructed such that the second portion of the system return signal has the first polarization state and the first portion of the system return signal has the second polarization state, the polarization rotator receives the first portion of the system return signal, and the outgoing LIDAR signal can have the second polarization state. In this example, the first LIDAR input signal and the second LIDAR input signal each has the second polarization state.

The above system configurations result in the first portion of the system return signal and the second portion of the system return signal being directed into different composite signals. As a result, since the first portion of the system return signal and the second portion of the system return signal are each associated with a different polarization state but electronics can process each of the composite signals, the LIDAR system compensates for changes in the polarization state of the LIDAR output signal in response to reflection of the LIDAR output signal.

The LIDAR adapter of FIG. 3 can include additional optical components including passive optical components. For instance, the LIDAR adapter can include an optional third lens 126. The third lens 126 can be configured to couple the second LIDAR output signal at a desired location. In some instances, the third lens 126 focuses or collimates the second LIDAR output signal at a desired location. For instance, the third lens 126 can be configured to focus or collimate the second LIDAR output signal on the facet 52 of the second comparative waveguide 50. The LIDAR adapter also includes one or more direction changing components 124 such as mirrors and prisms. FIG. 3 illustrates the LIDAR adapter including a mirror as a direction changing component 124 that redirects the second portion of the system return signal from the circulator 100 to the facet 52 of the second comparative waveguide 50 and/or to the third lens 126.

When the LIDAR system includes a LIDAR chip and a LIDAR adapter, the LIDAR chip, electronics, and the LIDAR adapter can be positioned on a common mount. Suitable common mounts include, but are not limited to, glass plates, metal plates, silicon plates and ceramic plates. As an example, FIG. 4 is a topview of a LIDAR system that includes the LIDAR chip and electronics 32 of FIG. 1A and the LIDAR adapter of FIG. 2 on a common support 140. Although the electronics 32 are illustrated as being located on the common support, all or a portion of the electronics can be located off the common support. When the light source 10 is located off the LIDAR chip, the light source can be located on the common support 140 or off of the common support 140. Suitable approaches for mounting the LIDAR chip, electronics, and/or the LIDAR adapter on the common support include, but are not limited to, epoxy, solder, and mechanical clamping.

The LIDAR systems can include components including additional passive and/or active optical components. For instance, the LIDAR system can include one or more components that receive the LIDAR output signal from the LIDAR chip or from the LIDAR adapter. The portion of the LIDAR output signal that exits from the one or more components can serve as the system output signal. As an example, the LIDAR system can include one or more beam steering components that receive the LIDAR output signal from the LIDAR chip or from the LIDAR adapter and that output all or a fraction of the LIDAR output signal that serves as the system output signal. Suitable beam steering components include, but are not limited to, movable mirrors, MEMS mirrors, and optical phased arrays (OPAs). In these instances, the one or more components can serve as a transmitter of the system output signal for the LIDAR system.

FIG. 5A through FIG. 5D illustrate an example of a suitable processing component for use as all or a fraction of the processing components selected from the group consisting of the processing component 22, the first processing component 46 and the second processing component 48. The processing component receives a comparative signal from a comparative waveguide 196 and a reference signal from a reference waveguide 198. The comparative waveguide 18 and the reference waveguide 20 shown in FIG. 1A and FIG. 1B can serve as the comparative waveguide 196 and the reference waveguide 198, the comparative waveguide 18 and the first reference waveguide 42 shown in FIG. 1C can serve as the comparative waveguide 196 and the reference waveguide 198, or the second comparative waveguide 50 and the second reference waveguide 44 shown in FIG. 1C can serve as the comparative waveguide 196 and the reference waveguide 198.

The processing component includes a second splitter 200 that divides the comparative signal carried on the comparative waveguide 196 onto a first comparative waveguide 204 and a second comparative waveguide 206. The first comparative waveguide 204 carries a first portion of the comparative signal to the light-combining component 211. The second comparative waveguide 208 carries a second portion of the comparative signal to the second light-combining component 212.

The processing component includes a first splitter 202 that divides the reference signal carried on the reference waveguide 198 onto a first reference waveguide 204 and a second reference waveguide 206. The first reference waveguide 204 carries a first portion of the reference signal to the light-combining component 211. The second reference waveguide 208 carries a second portion of the reference signal to the second light-combining component 212.

The second light-combining component 212 combines the second portion of the comparative signal and the second portion of the reference signal into a second composite signal. Due to the difference in frequencies between the second portion of the comparative signal and the second portion of the reference signal, the second composite signal is beating between the second portion of the comparative signal and the second portion of the reference signal.

The second light-combining component 212 also splits the resulting second composite signal onto a first auxiliary detector waveguide 214 and a second auxiliary detector waveguide 216. The first auxiliary detector waveguide 214 carries a first portion of the second composite signal to a first auxiliary light sensor 218 that converts the first portion of the second composite signal to a first auxiliary electrical signal. The second auxiliary detector waveguide 216 carries a second portion of the second composite signal to a second auxiliary light sensor 220 that converts the second portion of the second composite signal to a second auxiliary electrical signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).

In some instances, the second light-combining component 212 splits the second composite signal such that the portion of the comparative signal (i.e. the portion of the second portion of the comparative signal) included in the first portion of the second composite signal is phase shifted by 180° relative to the portion of the comparative signal (i.e. the portion of the second portion of the comparative signal) in the second portion of the second composite signal but the portion of the reference signal (i.e. the portion of the second portion of the reference signal) in the second portion of the second composite signal is not phase shifted relative to the portion of the reference signal (i.e. the portion of the second portion of the reference signal) in the first portion of the second composite signal. Alternately, the second light-combining component 212 splits the second composite signal such that the portion of the reference signal (i.e. the portion of the second portion of the reference signal) in the first portion of the second composite signal is phase shifted by 180° relative to the portion of the reference signal (i.e. the portion of the second portion of the reference signal) in the second portion of the second composite signal but the portion of the comparative signal (i.e. the portion of the second portion of the comparative signal) in the first portion of the second composite signal is not phase shifted relative to the portion of the comparative signal (i.e. the portion of the second portion of the comparative signal) in the second portion of the second composite signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).

The first light-combining component 211 combines the first portion of the comparative signal and the first portion of the reference signal into a first composite signal. Due to the difference in frequencies between the first portion of the comparative signal and the first portion of the reference signal, the first composite signal is beating between the first portion of the comparative signal and the first portion of the reference signal.

The first light-combining component 211 also splits the first composite signal onto a first detector waveguide 221 and a second detector waveguide 222. The first detector waveguide 221 carries a first portion of the first composite signal to a first light sensor 223 that converts the first portion of the second composite signal to a first electrical signal. The second detector waveguide 222 carries a second portion of the second composite signal to a second light sensor 224 that converts the second portion of the second composite signal to a second electrical signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).

In some instances, the light-combining component 211 splits the first composite signal such that the portion of the comparative signal (i.e. the portion of the first portion of the comparative signal) included in the first portion of the composite signal is phase shifted by 180° relative to the portion of the comparative signal (i.e. the portion of the first portion of the comparative signal) in the second portion of the composite signal but the portion of the reference signal (i.e. the portion of the first portion of the reference signal) in the first portion of the composite signal is not phase shifted relative to the portion of the reference signal (i.e. the portion of the first portion of the reference signal) in the second portion of the composite signal. Alternately, the light-combining component 211 splits the composite signal such that the portion of the reference signal (i.e. the portion of the first portion of the reference signal) in the first portion of the composite signal is phase shifted by 180° relative to the portion of the reference signal (i.e. the portion of the first portion of the reference signal) in the second portion of the composite signal but the portion of the comparative signal (i.e. the portion of the first portion of the comparative signal) in the first portion of the composite signal is not phase shifted relative to the portion of the comparative signal (i.e. the portion of the first portion of the comparative signal) in the second portion of the composite signal.

When the second light-combining component 212 splits the second composite signal such that the portion of the comparative signal in the first portion of the second composite signal is phase shifted by 180° relative to the portion of the comparative signal in the second portion of the second composite signal, the light-combining component 211 also splits the composite signal such that the portion of the comparative signal in the first portion of the composite signal is phase shifted by 180° relative to the portion of the comparative signal in the second portion of the composite signal. When the second light-combining component 212 splits the second composite signal such that the portion of the reference signal in the first portion of the second composite signal is phase shifted by 180° relative to the portion of the reference signal in the second portion of the second composite signal, the light-combining component 211 also splits the composite signal such that the portion of the reference signal in the first portion of the composite signal is phase shifted by 180° relative to the portion of the reference signal in the second portion of the composite signal.

The first reference waveguide 210 and the second reference waveguide 208 are constructed to provide a phase shift between the first portion of the reference signal and the second portion of the reference signal. For instance, the first reference waveguide 210 and the second reference waveguide 208 can be constructed so as to provide a 90 degree phase shift between the first portion of the reference signal and the second portion of the reference signal. As an example, one reference signal portion can be an in-phase component and the other a quadrature component. Accordingly, one of the reference signal portions can be a sinusoidal function and the other reference signal portion can be a cosine function. In one example, the first reference waveguide 210 and the second reference waveguide 208 are constructed such that the first reference signal portion is a cosine function and the second reference signal portion is a sine function. Accordingly, the portion of the reference signal in the second composite signal is phase shifted relative to the portion of the reference signal in the first composite signal, however, the portion of the comparative signal in the first composite signal is not phase shifted relative to the portion of the comparative signal in the second composite signal.

The first light sensor 223 and the second light sensor 224 can be connected as a balanced detector and the first auxiliary light sensor 218 and the second auxiliary light sensor 220 can also be connected as a balanced detector. For instance, FIG. 5B provides a schematic of the relationship between the electronics, the first light sensor 223, the second light sensor 224, the first auxiliary light sensor 218, and the second auxiliary light sensor 220. The symbol for a photodiode is used to represent the first light sensor 223, the second light sensor 224, the first auxiliary light sensor 218, and the second auxiliary light sensor 220 but one or more of these sensors can have other constructions. In some instances, all of the components illustrated in the schematic of FIG. 5B are included on the LIDAR chip. In some instances, the components illustrated in the schematic of FIG. 5B are distributed between the LIDAR chip and electronics located off of the LIDAR chip.

The electronics connect the first light sensor 223 and the second light sensor 224 as a first balanced detector 225 and the first auxiliary light sensor 218 and the second auxiliary light sensor 220 as a second balanced detector 226. In particular, the first light sensor 223 and the second light sensor 224 are connected in series. Additionally, the first auxiliary light sensor 218 and the second auxiliary light sensor 220 are connected in series. The serial connection in the first balanced detector is in communication with a first data line 228 that carries the output from the first balanced detector as a first data signal. The serial connection in the second balanced detector is in communication with a second data line 232 that carries the output from the second balanced detector as a second data signal. The first data signal is an electrical representation of the first composite signal and the second data signal is an electrical representation of the second composite signal. Accordingly, the first data signal includes a contribution from a first waveform and a second waveform and the second data signal is a composite of the first waveform and the second waveform. The portion of the first waveform in the first data signal is phase-shifted relative to the portion of the first waveform in the first data signal but the portion of the second waveform in the first data signal being in-phase relative to the portion of the second waveform in the first data signal. For instance, the second data signal includes a portion of the reference signal that is phase shifted relative to a different portion of the reference signal that is included the first data signal. Additionally, the second data signal includes a portion of the comparative signal that is in-phase with a different portion of the comparative signal that is included in the first data signal. The first data signal and the second data signal are beating as a result of the beating between the comparative signal and the reference signal, i.e. the beating in the first composite signal and in the second composite signal.

The electronics 32 includes a transform mechanism 238 configured to perform a mathematical transform on the first data signal and the second data signal. For instance, the mathematical transform can be a complex Fourier transform with the first data signal and the second data signal as inputs. Since the first data signal is an in-phase component and the second data signal its quadrature component, the first data signal and the second data signal together act as a complex data signal where the first data signal is the real component and the second data signal is the imaginary component of the input.

The transform mechanism 238 includes a first Analog-to-Digital Converter (ADC) 264 that receives the first data signal from the first data line 228. The first Analog-to-Digital Converter (ADC) 264 converts the first data signal from an analog form to a digital form and outputs a first digital data signal. The transform mechanism 238 includes a second Analog-to-Digital Converter (ADC) 266 that receives the second data signal from the second data line 232. The second Analog-to-Digital Converter (ADC) 266 converts the second data signal from an analog form to a digital form and outputs a second digital data signal. The first digital data signal is a digital representation of the first data signal and the second digital data signal is a digital representation of the second data signal. Accordingly, the first digital data signal and the second digital data signal act together as a complex signal where the first digital data signal acts as the real component of the complex signal and the second digital data signal acts as the imaginary component of the complex data signal.

The transform mechanism 238 includes a transform component 268 that receives the complex data signal. For instance, the transform component 268 receives the first digital data signal from the first Analog-to-Digital Converter (ADC) 264 as an input and also receives the second digital data signal from the first Analog-to-Digital Converter (ADC) 266 as an input. The transform component 268 can be configured to perform a mathematical transform on the complex signal so as to convert from the time domain to the frequency domain. The mathematical transform can be a complex transform such as a complex Fast Fourier Transform (FFT). A complex transform such as a complex Fast Fourier Transform (FFT) provides an unambiguous solution for the shift in frequency of LIDAR input signal relative to the LIDAR output signal that is caused by the radial velocity between the reflecting object and the LIDAR chip. The electronics use the one or more frequency peaks output from the transform component 268 for further processing to generate the LIDAR data (distance and/or radial velocity between the reflecting object and the LIDAR chip or LIDAR system). The transform component 268 can execute the attributed functions using firmware, hardware or software or a combination thereof.

Although FIG. 5A through FIG. 5B illustrate light-combining components that combine a portion of the reference signal with a portion of the comparative signal, the processing component can include a single light-combining component that combines the reference signal with the comparative signal so as to form a composite signal. As a result, at least a portion of the reference signal and at least a portion of the comparative signal can be combined to form a composite signal. The combined portion of the reference signal can be the entire reference signal or a fraction of the reference signal and the combined portion of the comparative signal can be the entire comparative signal or a fraction of the comparative signal.

As an example of a processing component that combines the reference signal and the comparative signal so as to form a composite signal, FIG. 5C illustrates the processing component of FIG. 5A modified to include a single light-combining component. The comparative waveguide 196 carries the comparative signal directly to the first light-combining component 211 and the reference waveguide 198 carries the reference signal directly to the first light-combining component 211.

The first light-combining component 211 combines the comparative signal and the reference signal into a composite signal. Due to the difference in frequencies between the comparative signal and the reference signal, the first composite signal is beating between the comparative signal and the reference signal. The first light-combining component 211 also splits the composite signal onto the first detector waveguide 221 and the second detector waveguide 222. The first detector waveguide 221 carries a first portion of the composite signal to the first light sensor 223 that converts the first portion of the second composite signal to a first electrical signal. The second detector waveguide 222 carries a second portion of the composite signal to the second light sensor 224 that converts the second portion of the second composite signal to a second electrical signal.

FIG. 5D provides a schematic of the relationship between the electronics, the first light sensor 223, and the second light sensor 224 of FIG. 5C. The symbol for a photodiode is used to represent the first light sensor 223, and the second light sensor 224 but one or more of these sensors can have other constructions. In some instances, all of the components illustrated in the schematic of FIG. 5D are included on the LIDAR chip. In some instances, the components illustrated in the schematic of FIG. 5D are distributed between the LIDAR chip and electronics located off of the LIDAR chip.

The electronics connect the first light sensor 223 and the second light sensor 224 as a first balanced detector 225. In particular, the first light sensor 223 and the second light sensor 224 are connected in series. The serial connection in the first balanced detector is in communication with a first data line 228 that carries the output from the first balanced detector as a first data signal. The first data signal is an electrical representation of the composite signal.

The electronics 32 include a transform mechanism 238 configured to perform a mathematical transform on the first data signal. The mathematical transform can be a real Fourier transform with the first data signal as an input. The electronics can use the frequency output from the transform as described above to extract the LIDAR data.

Each of the balanced detectors disclosed in the context of FIG. 5A through FIG. 5D can be replaced with a single light sensor. As a result, the processing component can include one or more light sensors that each receives at least a portion of a composite signal in that the received portion of the composite signal can be the entire composite signal or a fraction of the composite signal.

FIG. 5E shows an example of a relationship between the frequency of the LIDAR output signal and/or the system output signal, time, cycles and data periods. Although FIG. 5E shows frequency versus time for only one channel, the illustrated frequency versus time pattern can represent the frequency versus time for each of the channels. The base frequency of the LIDAR output signal (f_(o)) can be the frequency of the LIDAR output signal at the start of a cycle.

FIG. 5E shows frequency versus time for a sequence of two cycles labeled cycle_(j) and cycle_(j+1). In some instances, the frequency versus time pattern is repeated in each cycle as shown in FIG. 5E. The illustrated cycles do not include re-location periods and/or re-location periods are not located between cycles. As a result, FIG. 5E illustrates the results for a continuous scan.

Each cycle includes K data periods that are each associated with a period index k and are labeled DP_(k). In the example of FIG. 5E, each cycle includes three data periods labeled DP_(k) with k=1, 2, and 3. In some instances, the frequency versus time pattern is the same for the data periods that correspond to each other in different cycles as is shown in FIG. 5E. Corresponding data periods are data periods with the same period index. As a result, each data period DP₁ can be considered corresponding data periods and the associated frequency versus time patterns are the same in FIG. 5E. At the end of a cycle, the electronics return the frequency to the same frequency level at which it started the previous cycle.

During the data period DP₁, the electronics operate the light source such that the frequency of the LIDAR output signal changes by B₁ where B₁≠0. The duration of the frequency change during DP, is represented by T₁ where T₁>0. During the data period DP₂, the electronics operate the light source such that the frequency of the LIDAR output signal changes by B₂ where B₂≠0. The duration of the frequency change during DP₂ is represented by T₂ where T₂>0. The rate of frequency change during DP, can be represented by α₁ where α₁≠0. In FIG. 5E, the rate of frequency change during DP₁ (α₁) is linear with a value of B₁/T₁. The rate of frequency change during DP₂ can be represented by α₂ where α₂≠0. In FIG. 5E, the rate of frequency change during DP₂ (α₂) is linear with a value of B₂/T₂. During the data period DP₃, the electronics operate the light source such that the frequency of the LIDAR output signal is constant for the duration of the data period. The duration of DP₃ is represented by T₃ where T₃>0. The values of T₁, T₂, and T₃ can be the same or different. In some instances, T₁=T₂. In one example, T₁=T₂≠T₃. In another example, T₁=T₂=T₃. In some instances, T₁≠T₂.

The beat frequency of all or a portion of the beating signals selected from the first composite signal, the first data signal, the second composite signal, and the second data signal during the data period DP_(k) is F_(k) where k represents the data period index. For instance, when the processing component is constructed according to FIG. 5C and FIG. 5D, the beat frequency of the first composite signal and the first data signal is represented by F_(k). When the processing component is constructed according to FIG. 5A and FIG. 5B, the beat frequency of the first composite signal, the first data signal, the second composite signal, and the second data signal is represented by F_(k).

F₁ represents the beat frequency of the beating signals during the data period DP₁. The value of F₁ can include a contribution from the distance between the LIDAR system and the reflecting object (f_(r,1)) and a contribution from the radial velocity between the LIDAR system and a reflecting object (f_(d,1)). Accordingly, F₁ can be written as F₁=f_(r,1)+f_(d,1). The maximum possible value that can occur for F₁ under normal operating conditions of the LIDAR system is represented by F_(1max).

The beat frequency of the beating signals during the data period DP₂ is represented by F₂. The value of F₂ can include a contribution from the distance between the LIDAR system and a reflecting object (f_(r,2)) and a contribution from the radial velocity between the LIDAR system and the reflecting object (f_(d,2)). The maximum possible value that can occur for F₂ under normal operating conditions of the LIDAR system is represented by F_(2max).

The beat frequency of the beating signals during the data period DP₃ is represented by F₃. The maximum possible value that can occur for F₃ under normal operating conditions of the LIDAR system is represented by F_(3max). Since the frequency of the LIDAR output signal is constant during the data period DP₃, F₃ will have contribution from the radial velocity between the LIDAR system and the reflecting object (the Doppler frequency, f_(d,3)) but will not have a contribution from the distance between the LIDAR system and a reflecting object. As a result, the value of F₃ can be set to the value of the Doppler frequency (f_(d,3)) where f_(d,3)=2ν/λ with ν representing the radial velocity between the LIDAR system and a reflecting object with direction from the reflecting object toward the LIDAR system being the positive direction, λ and representing the wavelength of the LIDAR output signal. As a result, F₃=f_(d,3)=2ν/λ and F_(3max)=f_(dmax)=2ν_(max)/λ where f_(dmax) represents the maximum value of the Doppler frequency during operation of the LIDAR system under normal conditions and ν_(max) represents the maximum value of the radial velocity (ν) during normal operating conditions.

A portion of the variables described above are disclosed in the context of normal operating conditions. Normal operating conditions are the conditions for which the LIDAR system is designed to operate and are normally set out in the specifications for the LIDAR system. Accordingly, when specifications are available, the value of ν_(max) would represent the largest radial velocity set forth in the specifications. As another example, F_(1max) would represent the maximum in value of F₁ that can occur when operating the LIDAR system within the radial velocities and distances set forth in the specification.

The data period indices do not represent sequence in time. For instance, although FIG. 5E illustrates the cycles having DP₁ occurring before DP₂ and DP₃; the cycles can have other arrangements of data periods. Examples of cycles with different data period arrangements include, but are not limited to, cycles where DP₁ occurs between DP₂ and DP₃ or cycles where DP₃ occurs before DP₂ with DP₂ occurring before DP₁.

Before operating the LIDAR system so as to generate LIDAR data, the values of one or more operating parameters can be selected and/or calculated. The electronics can use the values identified for the one or more parameters in the generated of the LIDAR data. An example of one of these parameters is the Analog-to-Digital Converters (ADC) sample rate (f_(samp)). The processing components include one or more Analog-to-Digital Converters such as the first Analog-to-Digital Converter (ADC) 264 of FIG. 5A and FIG. 5C and the second Analog-to-Digital Converter (ADC) 266 of FIG. 5D. The one or more Analog-to-Digital Converters each receives one of the beating signals and are each sampled at an ADC sample rate (f_(samp)). The ADC sampling rates (f_(samp)) required to generate useful LIDAR data in prior LIDAR systems results may be impractical to achieve; however, the LIDAR system can be operated such that the electronics undersample the Analog-to-Digital Converter (ADC) 264 and/or the second Analog-to-Digital Converter (ADC) 266. The use of undersampling can permit the use of practical sampling rates.

The ADC sample rate (f_(samp)) can be selected such that f_(samp)≥2|F_(3max)|. Since F_(3max)=f_(dmax)=2ν_(max)/λ, the ADC sample rate (f_(samp)) can be selected such that f_(samp)≥2|F_(3max)|, or f_(samp)≥2|f_(dmax) or f_(samp)≥4ν_(max)/λ|. According to Nyquist's sampling theorem, the sampling rate for an Analog-to-Digital Converters (ADC) should be greater than or equal to twice the highest frequency in the beating signals. Accordingly, Nyquist's sampling theorem would provide a sample rate (f_(samp)) according to: f_(samp)≥2*max|F_(1max), F_(2max), F_(3max)|. A beating signal is considered oversampled when the sampling rate is greater than 2*max F_(1max), F_(2max), F_(3max) and undersampled when sampling rate is less than 2*max|F_(1max), F_(2max), F_(3max)|. The value of f_(samp) can be selected so the signal is undersampled. For instance, f_(samp) can be selected such that 2|F_(3max)|≤f_(samp)≤2*max|F_(1max), F_(2max), F_(3max)| or 2|f_(dmax)|≤f_(samp)≤2*max|F_(1max), F_(2max), F_(3max)| or 4|ν_(max)/λ|f_(samp)≤2*max|F_(1max), F_(2max), F_(3max)|.

Once an ADC sample rate (f_(samp)) is selected, the values for one or more other parameters can be identified for use in generating LIDAR data. For instance, a frequency spectrum can be defined according to FIG. 5F. As shown in FIG. 5F, the value of F₁ can vary between 0.0 and F_(1max). The frequency range from −F_(1max) to F_(1max) can be divided into multiple zones that each has a length equal to f_(samp). Each of the zones is associated with a zone index of k_(k) where the subscript k represents the data period index and each value of k_(k) is an integer. FIG. 5F illustrates the k_(k) values for data period DP1 (k₁). As shown in FIG. 5F, the value of k₁ can vary from −k_(1max) to k_(1max) to provide a total of 2*k_(1max)+1 values for k₁. In FIG. 5F, k_(1max) has a value of 2. The value for k_(1max) can be selected such that: (k_(1max)−0.5)f_(samp)≤F_(1max)<(k_(1max)+0.5)f_(samp).

The selected value of k_(1max) can be used to select a value for parameters p and q where p is an integer and q is an integer. The values of p and q are selected such that p<q, q>2k_(1max)+2, and p>q/(2k_(1max)+2). In some instances, p/q is an irreducible fraction. The selected values of p and q can be can be used to select B₁ and B₂ such that B₂=+/−(p/q)*B₁ or when T₁≠T₂, such that α₂=+/−(p/q)*α₁.

During operation of the LIDAR system, the one or more Analog-to-Digital Converters (ADCs) can each be sampled at a rate equal to f_(samp) and the frequency output from the transform component 268 in response to system output signal output from the LIDAR system during the data period DP₁ can serve as a value for F_(1,DC); the frequency output from the transform component 268 in response to system output signal output from the LIDAR system during the data period DP₂ can serve as a value for F_(2,DC); and the frequency output from the transform component 268 in response to system output signal output from the LIDAR system during the data period DP₃ can serve as the values of F_(3,DC).

The electronics can approximate the value of the contribution of the radial velocity between the LIDAR system and a reflecting object to the value F1 (f_(d,1)) as being equal to (f_(d,3)) and can approximate the value of the contribution of the radial velocity between the LIDAR system and the reflecting object to the value of F2 (f_(d,2)) as being equal to (f_(d,3)). Accordingly, the electronics can set f_(d,1)=f_(d,2)=f_(d,3). As noted above, f_(d,3)=F₃. Further, the electronics can approximate the value of F₃ as being equal to F_(3,DC) because F_(3DC) is not a result of undersampling because f_(samp)≥2|F_(3max)| which satisfies the Nyquist's sampling theorem during the data period DP₃. As a result, the electronics can approximate f_(d,1)=f_(d,2)=f_(d,3)=F₃=F_(3,DC)=f_(d).

Because of the undersampling of the ADC, there are multiple possible values for the contribution of the distance between the LIDAR system and the reflecting object to the value of F₁ (f_(r,1)) and there are multiple possible values for the contribution of the distance between the LIDAR system and the reflecting object to the value of F₂ (f_(r,2)). The electronics can determine the possible values of f_(r,1) for data period DP₁ and the possible values of f_(r,2) for the data period DP₂. Each of the different possible values can be represented by f_(r,k,n,e) where k represents the data period index, n is a possible value index in the range of −k_(1max)≤n≤k_(1max) where each value of n is an integer, and e represents an equation index that identifies the equation from which the possible value was generated. The electronics can determine a series of possible values for the data period DP₁ from the following Equation 1A: f_(r,1,n,A)=F_(1,DC)+f_(d)+n*f_(samp) where −k_(1max)≤n≤k_(1max). Accordingly, there can be 2*k_(1max)+1 values for f_(r,1,n,e). The electronics can determine a series of possible values for the data period DP₂ from the following Equation 2A: f_(r,2,n,A)=(F_(2,DC)+f_(d))*(q/p)+n*f_(samp)*(q/p) when the rate of frequency change during DP₂ (α₂) is positive or Equation 2B: f_(r,2,n,B)=−(F_(2,DC)+f_(d))*(q/p)−n*f_(samp)*(q/p) when the rate of frequency change during DP₂ (α₂) is positive where −k_(1max)≤n≤k_(1max). Accordingly, there can be (2*k_(1max)+1) values for f_(r,2,n,e).

One of the possible values of f_(r) determined from the data period DP₁ (f_(r,1,n,A) above) will match or substantially match one of the possible values of f_(r) determined from the data period DP₂ (f_(r,2,n,A) and f_(r,2,n,B)). The electronics can identify the matching pair. As a result of the conditions for selecting p and q, there will be only one matching pair for each cycle for values of n in the range of −k_(1max)≤n≤k_(1max). Values of n outside of this range can produce other matches. The value of f_(r) for the matching pair serves as the value of f_(r) for the cycle.

The electronics can use the values determined for f_(r) and/or f_(d) to determine the LIDAR data for the cycle. For instance, the electronics can quantify the distance between the object and the LIDAR system from c*f_(r)*T/(2*B₁) and/or the radial velocity between the object and the LIDAR system from ν=λ*f_(d)/2.

Although FIG. 5D illustrates three data periods, the number of data periods can be different. For instance, the data period DP₃ can be optional when the reflecting objects are stationary relative to the LIDAR system (i.e. ν=0.0). In these instances, the LIDAR data can be generated as disclosed above with f_(d,1)=f_(d,2)=f_(d,3)=f_(3,DC)=f_(d)=0.0.

Suitable platforms for the LIDAR chips include, but are not limited to, silica, indium phosphide, and silicon-on-insulator wafers. FIG. 6 is a cross-section of portion of a chip constructed from a silicon-on-insulator wafer. A silicon-on-insulator (SOI) wafer includes a buried layer 310 between a substrate 312 and a light-transmitting medium 314. In a silicon-on-insulator wafer, the buried layer 310 is silica while the substrate 312 and the light-transmitting medium 314 are silicon. The substrate 312 of an optical platform such as an SOI wafer can serve as the base for the entire LIDAR chip. For instance, the optical components shown on the LIDAR chips of FIG. 1A through FIG. 1D can be positioned on or over the top and/or lateral sides of the substrate 312.

FIG. 6 is a cross section of a portion of a LIDAR chip that includes a waveguide construction that is suitable for use in LIDAR chips constructed from silicon-on-insulator wafers. A ridge 316 of the light-transmitting medium extends away from slab regions 318 of the light-transmitting medium. The light signals are constrained between the top of the ridge 316 and the buried oxide layer 310.

The dimensions of the ridge waveguide are labeled in FIG. 6 . For instance, the ridge has a width labeled w and a height labeled h. A thickness of the slab regions is labeled T. For LIDAR applications, these dimensions can be more important than other dimensions because of the need to use higher levels of optical power than are used in other applications. The ridge width (labeled w) is greater than 1 μm and less than 4 μm, the ridge height (labeled h) is greater than 1 μm and less than 4 μm, the slab region thickness is greater than 0.5 μm and less than 3 μm. These dimensions can apply to straight or substantially straight portions of the waveguide, curved portions of the waveguide and tapered portions of the waveguide(s). Accordingly, these portions of the waveguide will be single mode. However, in some instances, these dimensions apply to straight or substantially straight portions of a waveguide. Additionally or alternately, curved portions of a waveguide can have a reduced slab thickness in order to reduce optical loss in the curved portions of the waveguide. For instance, a curved portion of a waveguide can have a ridge that extends away from a slab region with a thickness greater than or equal to 0.0 μm and less than 0.5 μm. While the above dimensions will generally provide the straight or substantially straight portions of a waveguide with a single-mode construction, they can result in the tapered section(s) and/or curved section(s) that are multimode. Coupling between the multi-mode geometry to the single mode geometry can be done using tapers that do not substantially excite the higher order modes. Accordingly, the waveguides can be constructed such that the signals carried in the waveguides are carried in a single mode even when carried in waveguide sections having multi-mode dimensions. The waveguide construction disclosed in the context of FIG. 6 is suitable for all or a portion of the waveguides on LIDAR chips constructed according to FIG. 1A through FIG. 1D.

Light sensors that are interfaced with waveguides on a LIDAR chip can be a component that is separate from the chip and then attached to the chip. For instance, the light sensor can be a photodiode, or an avalanche photodiode. Examples of suitable light sensor components include, but are not limited to, InGaAs PIN photodiodes manufactured by Hamamatsu located in Hamamatsu City, Japan, or an InGaAs APD (Avalanche Photo Diode) manufactured by Hamamatsu located in Hamamatsu City, Japan. These light sensors can be centrally located on the LIDAR chip. Alternately, all or a portion the waveguides that terminate at a light sensor can terminate at a facet located at an edge of the chip and the light sensor can be attached to the edge of the chip over the facet such that the light sensor receives light that passes through the facet. The use of light sensors that are a separate component from the chip is suitable for all or a portion of the light sensors selected from the group consisting of the first auxiliary light sensor 218, the second auxiliary light sensor 220, the first light sensor 223, and the second light sensor 224.

As an alternative to a light sensor that is a separate component, all or a portion of the light sensors can be integrated with the chip. For instance, examples of light sensors that are interfaced with ridge waveguides on a chip constructed from a silicon-on-insulator wafer can be found in Optics Express Vol. 15, No. 21, 13965-13971 (2007); U.S. Pat. No. 8,093,080, issued on Jan. 10, 2012; U.S. Pat. No. 8,242,432, issued Aug. 14, 2012; and U.S. Pat. No. 61,088,472, issued on Aug. 22, 2000 each of which is incorporated herein in its entirety. The use of light sensors that are integrated with the chip are suitable for all or a portion of the light sensors selected from the group consisting of the auxiliary light sensor 218, the second auxiliary light sensor 220, the first light sensor 223, and the second light sensor 224.

The light source 10 that is interfaced with the utility waveguide 12 can be a laser chip that is separate from the LIDAR chip and then attached to the LIDAR chip. For instance, the light source 10 can be a laser chip that is to the chip using a flip-chip arrangement. Use of flip-chip arrangements is suitable when the light source 10 is to be interfaced with a ridge waveguide on a chip constructed from silicon-on-insulator wafer. Alternately, the utility waveguide 12 can include an optical grating (not shown) such as Bragg grating that acts as a reflector for an external cavity laser. In these instances, the light source 10 can include a gain element that is separate from the LIDAR chip and then attached to the LIDAR chip in a flip-chip arrangement. Examples of suitable interfaces between flip-chip gain elements and ridge waveguides on chips constructed from silicon-on-insulator wafer can be found in U.S. Pat. No. 9,705,278, issued on Jul. 11, 2017 and in U.S. Pat. No. 5,991,484 issued on Nov. 23, 1999; each of which is incorporated herein in its entirety. When the light source 10 is a gain element or laser chip, the electronics 32 can change the frequency of the outgoing LIDAR signal by changing the level of electrical current applied to through the gain element or laser cavity.

Suitable electronics 32 can include, but are not limited to, a controller that includes or consists of analog electrical circuits, digital electrical circuits, processors, microprocessors, digital signal processors (DSPs), Field Programmable Gate Arrays (FPGAs), computers, microcomputers, or combinations suitable for performing the operation, monitoring and control functions described above. In some instances, the controller has access to a memory that includes instructions to be executed by the controller during performance of the operation, control and monitoring functions. Although the electronics are illustrated as a single component in a single location, the electronics can include multiple different components that are independent of one another and/or placed in different locations. Additionally, as noted above, all or a portion of the disclosed electronics can be included on the chip including electronics that are integrated with the chip.

Other embodiments, combinations and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. 

The invention claimed is:
 1. A LIDAR system, comprising: an Analog-to-Digital Converter (ADC) that receives a beating signal that beats a first signal against a second signal, the first signal being generated from light that has exited from the LIDAR system and returned to the LIDAR system after being reflected by an object located outside of the LIDAR system, the second signal being generated from light that has not exited from the LIDAR system, a frequency of the beating signal having a frequency contribution from a separation between the LIDAR system and the object; and electronics that generate multiple first possible frequency values that are each a candidate for a value of the frequency contribution, the electronics undersample the Analog-to-Digital Converter (ADC) so as to generate a digital data signal and use the digital data signal to quantify a distance between the object and the LIDAR system.
 2. The system of claim 1, wherein the electronics identify one of the first possible frequency values that represents a value of the frequency contribution from the separation between the LIDAR system and the object.
 3. The system of claim 1, wherein the electronics that generate multiple second possible frequency values that are each a candidate for a value of the frequency contribution.
 4. The system of claim 3, wherein only one of the first possible frequency values matches one of the second possible frequency values.
 5. The system of claim 4, wherein the electronics identify the first possible frequency value that matches one of the second possible frequency values.
 6. The system of claim 5, wherein the electronics use the identified frequency values to quantify a distance between the object and the LIDAR system.
 7. The system of claim 1, wherein the light that has exited from the LIDAR system is included in a system output signal, the electronics control a frequency of the system output signal over a series of cycles, the cycles include multiple data periods, the electronics change the frequency of the system output signal at a first rate during a first one of the data periods, the electronics change the frequency of the system output signal at a second rate during a second one of the data periods, the second rate is less than the first rate.
 8. The system of claim 7, wherein the second rate can be expressed as: α₂=+/−(p/q)*α₁ where α₂ represents the second rate, α₁ represents the first rate, p is an integer, q is an integer, and p<q, and p/q is an irreducible fraction.
 9. The system of claim 8, wherein q>2k_(1max)+2 and p>q/(2k_(1max)+2) wherein k_(1max) is an integer.
 10. The system of claim 9, wherein kimax is selected such that (k_(1max)−0.5)f_(samp)<F_(1max)≤(k_(1max)+0.5)f_(samp) where f_(samp) represents a sampling rate of the Analog-to-Digital Converter (ADC) and F_(1max) represents a maximum possible value of the beating signal during the first period.
 11. A LIDAR system, comprising: a transmitter configured to output a LIDAR output signal from the LIDAR system; and electronics that control a frequency of the system output signal over a series of cycles, the cycles include multiple data periods, the electronics changing the frequency of the system output signal at a first rate during a first one of the data periods, the electronics changing the frequency of the system output signal at a second rate during a second one of the data periods, the second rate being less than the first rate, the second rate can be expressed as: α₂=+/−(p/q)*α₁ where α₂ represents the second rate, α₁ represents the first rate, p is an integer, q is an integer, p<q, q>2k_(1max)+2, and k_(1max) is an integer.
 12. The system of claim 11, wherein p/q is an irreducible fraction.
 13. The system of claim 11, wherein q>2k_(1max)+2 wherein k_(1max) is an integer.
 14. The system of claim 11, wherein p>q/(2k_(1max)+2).
 15. The system of claim 14, wherein k_(1max)>0.
 16. The system of claim 11, wherein a₂=B₂/T and α₁=B₁/T where T represents a duration of the first data period, B₁ represents a frequency change of the system output signal during the first data period and B₂ represents a frequency change of the system output signal during the second data period.
 17. A method of operating a LIDAR system, comprising: receiving a beating signal at an Analog-to-Digital Converter (ADC), the beating signal beating a first signal against a second signal, the first signal being generated from light that has exited from the LIDAR system and returned to the LIDAR system after being reflected by an object located outside of the LIDAR system, the second signal being generated from light that has not exited from the LIDAR system, a frequency of the beating signal having a frequency contribution from a separation between the LIDAR system and the object; generating multiple first possible frequency values that are each a candidate for a value of the frequency contribution; and undersampling the Analog-to-Digital Converter (ADC) so as to generate a digital data signal and using the digital data signal to quantify a distance between the object and the LIDAR system.
 18. The method of claim 17, further comprising: identify one of the first possible frequency values that represents a value of the frequency contribution from the separation between the LIDAR system and the object.
 19. The method of claim 17, further comprising: generating multiple second possible frequency values that are each a candidate for a value of the frequency contribution.
 20. The method of claim 19, wherein only one of the first possible frequency values matches one of the second possible frequency values.
 21. The method of claim 20, further comprising: identifying the first possible frequency value that matches one of the second possible frequency values.
 22. The method of claim 21, further comprising: using the identified frequency values to quantify a distance between the object and the LIDAR system.
 23. A LIDAR system, comprising: an Analog-to-Digital Converter (ADC) that receives a beating signal that beats a first signal against a second signal, the first signal being generated from light that has exited from the LIDAR system and returned to the LIDAR system after being reflected by an object located outside of the LIDAR system, the second signal being generated from light that has not exited from the LIDAR system, a frequency of the beating signal having a frequency contribution from a separation between the LIDAR system and the object; electronics that generate multiple first possible frequency values that are each a candidate for a value of the frequency contribution, the light that has exited from the LIDAR system is included in a system output signal and the electronics control a frequency of the system output signal over a series of cycles, the cycles include multiple data periods, the electronics change the frequency of the system output signal at a first rate during a first one of the data periods, the electronics change the frequency of the system output signal at a second rate during a second one of the data periods, the second rate is less than the first rate, and the second rate can be expressed as: α₂=+/−(p/q)*α₁ where α₂ represents the second rate, α₁ represents the first rate, p is an integer, q is an integer, and p<q, and p/q is an irreducible fraction, q>2k_(1max)+2, p>q/(2k_(1max)+2), and k_(1max) is an integer.
 24. The system of claim 23, wherein the electronics identify the first possible frequency value that represents a value of the frequency contribution from the separation between the LIDAR system and the object.
 25. The system of claim 23, wherein the electronics that generate multiple second possible frequency values that are each a candidate for a value of the frequency.
 26. The system of claim 25, wherein only one of the first possible frequency values matches one of the second possible frequency values.
 27. The system of claim 26, wherein electronics identify the first possible frequency value that matches one of the second possible frequency values.
 28. The system of claim 27, wherein the electronics use the identified frequency values to quantify a distance between the object and the LIDAR system.
 29. The system of claim 23, wherein k_(1max) is selected such that (k_(1max)−0.5)f_(samp) F_(1max)≤(k_(1max)+0.5)f_(samp) where f_(samp) represents a sampling rate of the Analog-to-Digital Converter (ADC) and F_(1max) represents a maximum possible value of the beating signal during the first period.
 30. A method of operating a LIDAR system, comprising: outputting a LIDAR output signal from the LIDAR system; and controlling a frequency of the system output signal over a series of cycles, the cycles include multiple data periods, controlling the frequency including changing the frequency of the system output signal at a first rate during a first one of the data periods, controlling the frequency including changing the frequency of the system output signal at a second rate during a second one of the data periods, the second rate being less than the first rate, and the second rate can be expressed as: α₂=+/−(p/q)*α₁ where α₂ represents the second rate, α₁ represents the first rate, p is an integer, q is an integer, p<q, q>2k_(1max)+2, and k_(1max) is an integer.
 31. The method of claim 30, wherein p/q is an irreducible fraction.
 32. The method of claim 30, wherein q>2k_(1max)+2 wherein k_(1max) is an integer.
 33. The method of claim 30, wherein p>q/(2k_(1max)+2).
 34. The method of claim 33, wherein k_(1max)>0.
 35. The method of claim 30, wherein α₂=B₂/T and α₁=B₁/T where T represents a duration of the first data period, B₁ represents a frequency change of the system output signal during the first data period and B₂ represents a frequency change of the system output signal during the second data period. 